#include<stdio.h>
int main()
{
    printf("please enter n:");
    int n;
    scanf("%d",&n);
    long long fact=1;
    int i=1;
    while (i<=n)
    {
        fact = fact * i;
        i=i+2;
    }
    printf("%d!=%ld\n",n,fact);
    printf("over!");

    return 0;    
}